1. Field of the Invention
The present invention relates to an operating method, and more particularly, to an operating method utilized on an alternating current (AC) light-emitting diode (LED).
2. Description of Related Art
LEDs have been widely applied in different fields with the continuous development of optoelectronic technology. The conventional LED chip is driven by a direct current (DC) power. A control circuit converting AC to DC and buck components are necessary for operating the conventional DC LED, since the AC power is widely utilized in our daily life. Thus, the conventional DC LED manufacturing cost would increase and the operational efficiency may be negatively affected. After year 2005, more and more AC LED chips have been released by the manufacturers.
Since the AC LED may operate with a starting voltage, the AC driving voltage has to surpass the starting voltage to turn on the AC LED. Meanwhile, also as the result of the starting voltage, a driving current waveform of the AC LED would change to a non-sinusoidal driving current signal waveform, increasing the difficulty for the measurement of the driving current of the AC LED. Furthermore, since the brightness of the AC LED may vary according to different driving current, the quality control for the AC LED may be more of a difficult task without the steady driving current.
Please refer to FIG. 1 where a circuit diagram of an AC LED is demonstrated.
The AC LED circuit 1 includes an AC power 10, an AC LED 11, and a resistor 12 connected in series. The AC power 10 could provide a driving voltage for triggering the AC LED 11 and adjust a driving current passing through the AC LED 11 by the resistor 12.
Please refer to FIG. 2 where an AC LED detecting circuit diagram is demonstrated.
The detecting circuit 2 comprises an AC power 21 and AC LED 22 connected in series. The AC power 21 provides an AC driving voltage and current. For the quality control purpose such as screening and grouping the AC LEDs, a consistent driving current as a threshold may be necessary.
The conventional detecting method for the AC LED 22 is an approach of trial and error, which applies a randomly selected AC testing voltage to the detecting circuit 2 for measuring a corresponding testing driving current. By repeatedly adjusting the value of the applied AC testing voltage, an AC testing voltage corresponding to a predetermined testing current could be obtained.
An improved testing method for the AC LED would select an AC LED (such as the AC LED 22) as a benchmark and determine a peak driving voltage Vp associated with a predetermined driving current Irms and a peak driving current Ip of the selected AC LED 22. The peak driving current Ip is thereafter applied to other AC LEDs for obtaining their corresponding peak driving voltages Vp. However, if the electrical characteristic of the selected AC LED 22 is not located at the middle of electrical characteristic distribution of all AC LEDs, the measurement for other AC LEDs on basis of the peak driving current Ip of the selected AC LED 22 may deviate.